分治1--二分查找

分治1--二分查找

一、心得

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二、題目和分析

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三、代碼和結果

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#include <iostream>
using namespace std;
int a[10]={1,2,4,5,7,8,9,10,13,20};


//非遞歸 
int find(int i){
    int l=0,r=9;
    int mid=(l+r)/2;
    while(l<=r){
        mid=(l+r)/2;
        if(a[mid]==i) return mid;
        else if(i<a[mid]){
            r=mid-1;
            //cout<<"l:"<<l<<" "<<"rr:"<<r<<endl;
        }
        else{
            l=mid+1;
            //cout<<"ll:"<<l<<" "<<"r:"<<r<<endl;
        }
    }
    return -1;
}
//遞歸
int find_recusion(int i,int l,int r){
    if(l<=r){
        int mid=(l+r)/2;
        if(a[mid]==i) return mid;
        else if(i<a[mid]){
            find_recusion(i,l,mid-1);
        }
        else{
            find_recusion(i,mid+1,r);
        }
        
    }
    else{
        return -1;
    } 
    
    
} 


int main(){
    
    cout<<find(20)<<endl;
    cout<<find_recusion(20,0,9)<<endl;
    cout<<find(3)<<endl;
    cout<<find_recusion(3,0,9)<<endl;
    cout<<find(2)<<endl;
    cout<<find_recusion(2,0,9)<<endl;
    return 0;
}